Various surfaces are used to facilitate control of a craft's direction while in flight. The ability to control flight characteristics produces a stable flight path and permits controlled guidance of the craft. Flight controls typically include ailerons, an elevator, and a rudder. Flight controls in projectiles may be as simple as comprising a set of tail fins in order to maintain stable flight along a desired path.
Many projectiles are fired or launched through a tube or barrel necessitating the need for any control surfaces to not impede the projectile's path. In order to accommodate this requirement, projectiles will often utilize deployable control surfaces that extend outwards from the projectile after launch. It is necessary to control when these surfaces are extended otherwise the control surfaces could cause damage to neighboring structures during launch.